This invention relates to catalyst materials, their preparation and their use in olefin polymerization.
The use of metallocenes, e.g. cyclopentadienyl or indenyl complexes of metals such as Ti, Zr and Hf, in olefin polymerization catalyst systems is well known.
Metallocene procatalysts are generally used as part of a catalyst system-which also includes an ionic cocatalyst or catalyst activator, for example an aluminoxane (e.g. methylaluminoxane (MAO), hexaisobutylaluminoxane, and tetraisobutylaluminoxane) or a boron compound (e.g. a fluoroboron compound such as triphenylpentafluoroboron (B(C6F5)3) or triphenylcarbenium tetraphenylpentafluoroborate ((C6H5)3C+Bxe2x88x92(C6F5)4)).
However, where a metallocene procatalyst which does not contain alkyl (especially methyl) ligands is used, it is necessary to react the procatalyst with a material which serves to introduce alkyl ligands. MAO can perform this function but in the case of non-aluminoxane cocatalysts it is necessary to react the metallocene with an alkylating agent so as to introduce the alkyl ligands.
This however has the disadvantage that the alkylated metallocene has to be separated from the excess reagents and by-products and purified before being heterogenised, ie. loaded onto a catalyst support.
It has now been found that alkylation of certain procatalysts, e.g. metallocene procatalysts may be effected in a particularly simple and straightforward manner by loading the procatalyst onto a particulate catalyst support which has been pre-treated with an alkylating agent.
Thus viewed from one aspect the invention provides a process for the preparation of a catalyst material, said process comprising the steps of:
(a) treating a particulate support material with an alkylating agent;
(b) contacting the alkylating agent treated support material with a procatalyst, e.g. a metallocene procatalyst; optionally
(c) contacting the support material with an ionic catalyst activator; and optionally
(d) recovering the catalyst-carrying support material.
In the process of the invention, the particulate support material is preferably an inorganic material, especially preferably a metal or pseudo metal oxide such as silica, alumina or zirconia or a mixed oxide such as silica-alumina, in particular silica, alumina or silica-alumina. Particularly preferably, the support material is acidic, e.g. having an acidity greater than or equal to silica, more preferably greater than or equal to silica-alumina and even more preferably greater than or equal to alumina. The acidity of the support material can be studied and compared using the TPD (temperature programmed desorption of gas) method. Generally the gas used will be ammonia. The more acidic the support, the higher will be its capacity to adsorb ammonia gas. After being saturated with ammonia, the sample of support material is heated in a controlled fashion and the quantity of ammonia desorbed is measured as a function of temperature.
Especially preferably the support is a porous material so that the metallocene may be loaded into the pores of the support, e.g. using a process analogous to those described in WO94/14856 (Mobil), WO95/12622 (Borealis) and WO96/00243 (Exxon). The particle size is not critical but is preferably in the range 5 to 200 xcexcm, more preferably 20 to 80 xcexcm.
Before treatment with the alkylating agent, the particulate support material is preferaby calcined, ie heat treated, preferably under a non-reactive gas such as nitrogen. This treatment is preferably at a temperature in excess of 100xc2x0 C., more preferably 200xc2x0 C. or higher, e.g. 200-700xc2x0 C., particularly about 300xc2x0 C. The calcination treatment is preferably effected for several hours, e.g. 2 to 30 hours, more preferably about 10 hours. It is thought that this calcination has the effect of optimizing the reaction of the alkylating agent with acid hydroxyl groups on the support material.
The treatment of the support with the alkylating agent may be effected using an alkylating agent in a gas or liquid phase, e.g. in an organic solvent for the alkylating agent. The alkylating agent may be any agent capable of introducing alkyl groups, preferably C1-6 alkyl groups and most especially preferably methyl groups. Such agents are well known in the field of synthetic organic chemistry. Preferably the alkylating agent is an organometallic compound, especially an organoaluminium compound (such as trimethylaluminium (TMA), dimethyl aluminium chloride, triethylaluminium) or a compound such as methyl lithium, dimethyl magnesium, triethylboron, etc.
The quantity of alkylating agent used will depend upon the number of active sites on the surface of the carrier. Thus for example, for a silica support, surface hydroxyls are capable of reacting with the alkylating agent. In general, an excess of alkylating agent is preferably used with any unreacted alkylating agent subsequently being washed away.
Where an organoaluminium alkylating agent is used, this is preferably used in a quantity sufficient to provide a loading of at least 0.1 mmol Al/g carrier, especially at least 0.5 mmol Al/g, more especially at least 0.7 mmol Al/g, more preferably at least 1.4 mmol Al/g carrier, and still more preferably 2 to 3 mmol Al/g carrier. Where the surface area of the carrier is particularly high, lower aluminium loadings may be used. Thus for example particularly preferred aluminium loadings with a surface area of 300-400 m2/g carrier may range from 0.5 to 3 mmol Al/g carrier while at surface areas of 700-800 m2/g carrier the particularly preferred range will be lower.
Following treatment of the support material with the alkylating agent, the support is preferably removed from the treatment fluid and any excess treatment fluid is allowed to drain off.
The treated support material is then loaded with the procatalyst, preferably using a solution of the procatalyst in an organic solvent therefor, e.g. as described in the patent publications referred to above. Preferably, the volume of procatalyst solution used is from 50 to 500% of the pore volume of the carrier, more especially preferably 80 to 120%. The concentration of procatalyst compound in the solution used can vary from dilute to saturated depending on the amount of metallocene active sites that it is desired be loaded into the carrier pores.
The metal of the procataylst may be any metal effective in olefin polymerization, e.g. a metal of group 3 to 8, especially preferably a transition metal or lanthanide, in particular Ti, Zr or Hf.
The procatalyst of use according to the invention may be a metallocene or a non-metallocene although metallocene procataylsts are preferred.
Where the procatalyst is a non-metallocene, i.e does not comprise a cyclopentadienyl ligand or ligand derived from a cyclopentadienyl moiety such as indenyl, the metal atom is coordinated by at least one suitable sigma or xcex7 bonding ligand, preferably a xcex7 bonding ligand. In a preferred embodiment the xcex7 bonding ligand is a heterocyclic group, especially one comprising a fused ring system. In a most preferred embodiment said ring system comprises 3 nitrogen atoms attached to the same carbon atom, one of said atoms forming part of two fused rings. Suitable heterocyclic ligands of this type are of formula 
where groups R1, R2, R3 and R4 are the same or different selected from the group of H, C1-C12 alkyl, alkenyl, aryl (phenyl preferable), alkylaryl, or the groups R1, R2, R3 and R4 may contain silicon atoms instead of one or more carbon atoms, preferably they are SiH3, SiH2R5, SiHR6R3, SiR8R9R10 groups where groups R5 to R10 are also the groups recited above. The substituent groups may be also a combination of several groups recited above. R1 to R4 can also be taken together to form bridged structures. In the presence of a base a balance exists in the formula (2) between two ionic isomeric structures which are presented in the right of the formula (2). Formula (2) preferably represents a triaza bicyclo alkenyl, more preferably a 1,5,7-triazabicyclodec-5-enyl, most preferably a 1,5,7-triaza (4.4.0) bicyclodec-5-enyl.
The non-metallocene may have one or preferably more (e.g. 2 or 3) xcex7-bonding groups and where more than one such group is present these may be linked by a bridging group, e.g. a group providing a 1, 2 or 3 atom chain between such xcex7-bonding groups.
The xcex7-bonding ligands in such non-metallocenes may be simple unsubstituted ligands, but preferably they will be optionally substituted fused ring systems.
The procataylst is however preferably a metallocene. The metallocene procatalyst is preferably a halide, more especially preferably a chloride.
The metallocene may have one or preferably more (e.g. 2 or 3) xcex7-bonding groups and where more than one such group is present these may be linked by a bridging group, e.g. a group providing a 1, 2 or 3 atom chain between such xcex7-bonding groups. The xcex7-bonding groups may be cyclopentadienyl groups optionally carrying ring substituents which may be pendant groups, fused rings, bridging groups to other cyclopentadienyl rings or groups which themselves directly coordinate the metal. Such ligands are well known from the technical and patent literature relating to metallocene olefin polymerization catalysts, e.g. EP-A-35242 (BASF), EP-A-129368 (Exxon), EP-A-206794 (Exxon), PCT/FI97/00049 (Borealis), EP-A-318048, EP-A-643084, EP-A-69951, EP-A-410734 and EP-A-128045.
The xcex7-bonding ligands in such metallocenes may be simple unsubstituted cyclopentadienyl rings, but preferably they will be optionally substituted fused ring systems (eg. indenyl ligands), substituted cyclopentadienyl rings, optionally substituted bridged bis-cyclopentadienyl ligands or optionally substituted bridged bis fused ring systems (eg. bis indenyl ligands). Suitable examples are discussed for example in EP-B-35242 (BASF), EP-B-129368 (Exxon) and EP-B-206794 (Exxon).
Examples of metallocene procatalysts which may be used in the process of the invention include the metallocene compounds with a one or two atom long bridge joining the cyclopentadienyl rings, eg. a ethylene bridge or a bridge R2X where X is carbon or silicon and R is alkyl, aryl, aralkyl, etc. (for example a methyl, benzyl, etc group typically containing up to 10 carbons). Preferably, a ring position on the cyclopentadienyl rings adjacent the bridge attachment position is substituted, for example by an alkyl group such as methyl. The metal of the metallocene may conveniently be any group 3 to 8 metal, preferably titanium, zirconium or hafnium. Examples of such metallocenes include:
dimethyl-silyl{bis-(2-methyl-4-tert.butyl)}zirconium-dichloride;
dimethyl-silyl{bis-(2-methyl-4-phenyl-indenyl)}zirconium-dichloride;
dimethyl-silyl{bis-(2-methyl-4-naphthyl-indenyl)}zirconium-dichloride;
dimethyl-silyl{bis-(2-methyl-4,6-di-isopropyl-indenyl)}zirconium-dichloride;
dimethyl-silyl{bis-(2-methyl-4,7-dimethyl-indenyl)}zirconium-dichloride;
dimethyl-silyl{bis-(2-methyl-benz[e]-indenyl)}zirconium-dichloride;
dimethyl-silyl{bis-(fluorenyl)}zirconium-dichloride;
rac-[ethylenebis(2-(tert)-butyldimethylsiloxy)indenyl)]-zirconium-dichloride;
dimethyl-silyl{bis-(2-methyl-4-tert.butyl)}hafnium-dichloride;
dimethyl-silyl{bis-(2-methyl-4-phenyl-indenyl)}hafnium-dichloride;
dimethyl-silyl{bis-(2-methyl-4-naphthyl-indenyl)}hafnium-dichloride;
dimethyl-silyl{bis-(2-methyl-4,6-di-isopropyl-indenyl)}hafnium-dichloride;
dimethyl-silyl{bis-(2-methyl-4,7-dimethyl-indenyl)}hafnium-dichloride;
dimethyl-silyl{bis-(2-methyl-benz[e]-indenyl)}hafnium-dichloride;
dimethyl-silyl{bis-(fluorenyl)}hafnium-dichloride; and
rac-[ethylenebis(2-(tert)-butyldimethylsiloxy)indenyl)]-hafnium-dichloride.
A further class of metallocene procatalyst used in the process of the invention are the xcex7-bonding metal complexes of ligands which contain a xcex7-bonding component (eg. a cyclopentadienyl ring or an analog such as an indenyl ring) and a component (eg. a side chain) capable of co-ordinating to the metal in a non xcex7-bonding fashion.
The metal in such complexes will again conveniently be an ion of a transition metal or lanthanide e.g. a group 3 to 8 metal, for example titanium or zirconium. Examples of such complexes include:
1,2,3,4-tetramethyl,5-(dimethylsilyl-{(tert)-butyl-amido)}(cyclopentadienyl)titanium-dichloride;
1,2,3,4-tetramethyl,5-(dimethylsilyl-{(tert)-butyl-amido)}(cyclopentadienyl)zirconium-dichloride; and
1,2,3,4-tetramethyl,5-(ethylene-{(tert)-butyl-amido)}(cyclopentadienyl)titanium-dichloride.
Another class of metallocene procatalyst which may be used in the process of the invention comprises compounds having one cyclopentadienyl ligand in conjunction with another ligand; eg. (cyclopentadienyl-hydrido-boro-trispyrazol)-zirconium dichloride. (Other such materials are disclosed in WO97/17379 (Borealis) and the publications referred to therein).
The metallocene procatalyst may conveniently be a metallocene in which the cyclopentadienyl (or equivalent, eg. indenyl, etc) groups are not joined by a bridge or where the cyclopentadienyl rings are joined by a bridge but the ring positions adjacent the bridge attachment site are unsubstituted. Again the metal may be a transition metal or lanthanide e.g. a group 3 to 8 metal, eg. zirconium. Example of such metallocenes include:
rac-ethylene-bis(1-indenyl)zirconium dichloride;
rac-ethylene-bis(4,5,6,7-tetrahydro-1-indenyl)-zirconium dichloride;
bis(n-butylcyclopentadienyl)zirconium dichloride;
bis(1,2-dimethylcyclopentadienyl)zirconium dichloride;
bis(1,3-dimethylcyclopentadienyl)zirconium dichloride;
bis(4,7-dimethylindenyl)zirconium dichloride;
bis(1,2-ethyl,methylcyclopentadienyl)zirconium dichloride;
bisfluorenylzirconium dichloride;
bisindenylzirconium dichloride;
biscyclopentadienylzirconium dichloride; and
bistetrahydroindenylzirconium dichloride.
The active metal (ie. the metal of the procatalyst) is preferably loaded onto the support material at from 0.1 to 4%, preferably 0.5 to 3.0%, especially 1.0 to 2.0%, by weight metal relative to the dry weight of the support material.
After loading of the procatalyst onto the support material, the loaded support may be recovered for use in olefin polymerization, e.g. by separation of any excess procatalyst solution and if desired drying of the loaded support, optionally at elevated temperatures, e.g. 25 to 80xc2x0 C.
Alternatively, a non-MAO cocatalyst, e.g. an ionic catalyst activator (such as a boron or aluminium compound, especially a fluoroborate) may also be mixed with or loaded onto the catalyst support material. This may be done simultaneously or more preferably subsequently to loading of the procatalyst, for example by including the further catalyst, cocatalyst or catalyst activator in the solution of the procatalyst or preferably, by contacting the procatalyst loaded support material with a solution of the further catalyst, cocatalyst or catalyst activator, e.g. a solution in an organic solvent. Alternatively however any such further material may be added to the procatalyst loaded support material in the polymerization reactor or shortly before dosing of the catalyst material into the reactor.
In this regard, it is particularly preferred to use a fluoroborate catalyst activator, especially a B(C6F5)3 or more especially a 6B(C6F5)4 compound, such as B(C6F5)3, C6H5N(CH3)2H:B(C6F5)4 or (C6H5)3C:B(C6F5)4.
Where such a catalyst activator is used, it is preferably used in a mole ratio to the metallocene of from 0.1:1 to 100:1, especially 1:1 to 0.50:1, particularly 2:1 to 30:1.
Where the further material is loaded onto the procatalyst loaded support material, the support may be recovered and if desired dried before use in olefin polymerization.
The procatalyst loaded support material is novel and forms a further aspect of the invention. Viewed from this aspect the invention provides an olefin polymerization catalyst material comprising a procatalyst-loaded, e.g. metallocene loaded, alkylating agent pre-treated particulate support material, preferably a porous inorganic support material.
Viewed from a yet further aspect the invention provides a method of olefin polymerization wherein polymerization is effected in the presence of a catalyst material comprising a procatalyst-loaded, e.g. metallocene-loaded support material, characterised in that said support material comprises a procatalyst-loaded alkylating agent pre-treated particulate support material, preferably a porous inorganic support material.
In the method of the invention the catalyst material preferably also comprises a non-MAO, more preferably a non-aluminoxane, ionic catalyst activator, in particular a boron compound, especially a fluoroborate compound.
The olefin polymerized in the method of the invention is preferably an alpha-olefin or a mixture of alpha olefins, for example C2-20 olefins, e.g. ethylene, propene, n-but-1-ene, n-hex-1-ene, 4-methyl-pent-1-ene, n-oct-1-ene- etc. The olefins polymerized in the method of the invention may include any compound which includes unsaturated polymerizable groups. Thus for example unsaturated compounds, such as C6-20 olefins, and polyenes, especially C6-20 dienes, may be included in a comonomer mixture with lower olefins, e.g. C2-5 xcex1-olefins. Diolefins (ie. dienes) are suitably used for introducing long chain branching into the resultant polymer. Examples of such dienes include xcex1,xcfx89 linear dienes such as 1,5-hexadiene, 1,6-heptadiene, 1,8-nonadiene, 1,9-decadiene, etc.
In general, where the polymer being produced is a homopolymer it will preferably be polyethylene or polypropylene. Where the polymer being produced is a copolymer it will likewise preferably be an ethylene or propylene copolymer with ethylene or propylene making up the major proportion (by number and more preferably by weight) of the monomer residues. Comonomers, such as C4-6 alkenes, will generally be incorporated to contribute to the mechanical strength of the polymer product.
If desired, the nature of the monomer/monomer mixture and the polymerization conditions may be changed during the polymerization process so as to produce a broad bimodal or multimodal molecular weight distribution (MWD) in the final polymer product. In such a broad MWD product, the higher molecular weight component contributes to the strength of the end product while the lower molecular weight component contributes to the processability of the product, e.g. enabling the product to be used in extrusion and blow moulding processes, for example for the preparation of tubes, pipes, containers, etc.
A multimodal MWD can be produced using a catalyst material with two or more different types of active polymerization sites, e.g. with one such site provided by the metallocene on the support and further sites being provided by further catalysts, e.g. Ziegler catalysts, other metallocenes, etc. included in the catalyst material as discussed above.
Polymerization in the method of the invention may be effected in one or more, e.g. 1, 2 or 3, polymerization reactors, using conventional polymerization techniques, e.g. gas phase, solution phase and slurry polymerization.
For slurry reactors, the reaction temperature will generally be in the range 60 to 110xc2x0 C. (e.g. 85-110xc2x0 C.), the reactor pressure will generally be in the range 5 to 80 bar (e.g. 50-65 bar), and. the residence time will generally be in the range 0.3 to 5 hours (e.g. 0.5 to 2 hours). The diluent used will generally be an aliphatic hydrocarbon having a boiling point in the range xe2x88x9270 to +100xc2x0 C. In such reactors, polymerization may if desired be effected under supercritical conditions.
For gas phase reactors, the reaction temperature used will generally be in the range 60 to 115xc2x0 C. (e.g. 70 to 110xc2x0 C.), the reactor pressure will generally be in the range 10 to 25 bar, and the residence time will generally be 1 to 8 hours. The gas used will commonly be a non-reactive gas such as nitrogen together with monomer (e.g. ethylene).
For solution phase reactors, the reaction temperature used will generally be in the range 130 to 270xc2x0 C., the reactor pressure will generally be in the range 20 to 400 bar and the residence time will generally be in the range 0.1 to 1 hour. The solvent used will commonly be a hydrocarbon with a boiling point in the range 80-200xc2x0 C.
Generally the quantity of catalyst used will depend upon the nature of the catalyst, the reactor types and conditions and the properties desired for the polymer product. Conventional catalyst quantities, such as described in the publications referred to herein, may be used.